Single side-band system



July 19, 1949. B. E. LENEHAN SINGLE SIDE-BAND SYSTEM Filed Oct. 20, 1945Receiver INVENTOR ATTORNEY Bernard ELen/mn ml. J/

Fig. 2.

Amplifier WITNESSES y 042/ Osczllai'or Patented July 19, I949 SINGLESIDE-BAND SYSTEM Bernard E. Lenehan, Bloomfield, N. J., assignor toWestinghouse Electric Corporation,

East

Pittsburgh, Pa., a corporation of Pennsylvania Application October 20,1945, Serial No. 623,594

24 Claims.

This invention relates to systems for transmitting signals, and it hasparticular relation to single sideband systems.

The advantages of single side-bandtransmission are well known in theart. For example, reference may be made to the Radio EngineeringHandbook, Third Edition, by Keith Henney. 1941, pages 552 and 553. Thishandbook is published by the McGraw-Hill Book Company of New York city.However, the size, cost and com plexity of the equipment required forsingle sideband systems designedin accordance with the prior art havediscouraged extensive commercial utilization of the system.

In accordance with the invention, an improved and simplified singleside-band system is provided for transmitting signals. Transmission maybe efiected over any desired channel. For example, the transmission maybe effected by the pro-pogation of radiation through space, that is,radio, or it may be effected over conductors.

A signal transmitted by systems embodying the invention may be employedfor any desired function. For example, the signals may be employed forcommunication purposes, for relaying purposes, for telemetering purposesor for supervisory control of any desired equipment.

The invention contemplates the provision of a polyphase carrier whereinthe phase components of the carrier are displaced by a substantialangle. In addition, the signal-to-be-transmitted is also produced inpolyphase form wherein the phase components are displaced bysubstantially the same angle present between the phase components of thecarrier. Each component of the signal to be transmitted modulates aseparate one of the carrier components in a suitable modulator.

Preferably the modulator is of the balanced type in order to suppressthe carrier component. The outputs of the two modulators consistrespectively of the sum and difference of the upper and lower side bandsformed by the modulation of the carrier. By suitably adding orsubtracting the outputs of the two modulators, either the upper or thelower side band alone may be produced.

In systems embodying the invention, three major problems are present.The balanced modulator must be adequately balanced in order to suppresssubstantially the carrier supplied thereto. In addition, the outputs ofthe two modulators must be properly related to effect substantialcancellation of one of the side-bands produced thereby. Finally,adequate equipment must be provided for producing the phase componentsof the carrier and signal. If phase shifters are through appropriaterectifier-s in the modulator..

CancellatiOn of one of the side-bands produced by the two modulators insystems embodying the invention is facilitated by the provision ofadjustments for controlling the amplitudes of the outputs derived fromthe two modulators.

In order to provide polyphase carrier and signal quantities, phaseshifters are hereinafter illustrated and described which maintain theamplitude and phase displacement of related components substantiallyconstant over the entire frequency range desired. The phase shifters areof the static type employing only resistors, capacitors and inductanceelements.

It is, therefore, an object of the invention to provide an improvedsystem for transmitting signals.

It is a further object oi the invention to provide an improved singleside-hand transmitter.

It is a further object of the invention to provide a single side bandtransmitter employing barrierlayer modulators.

It is also an object of the invention to provide means for adjusting theimpedance distribution of a barrier-layer modulator.

It is an additional object of the invention to provide means foradjusting the extent of sup-,

pression of a carrier in a modulator.

It is a still further object of the invention to provide means foradjusting the extent of cancellation of a side band in a phase-rotation,single-side-band transmitter.

Additional objects of the invention will be apparent from the followingdiscussion taken in conjunction with the accompanying drawing in which:

Figure 1 is a schematic view or a system embodying the invention.

Fig. 2 is a schematic view showing a modified output unit suitable forthe system of Fig. 1, and

Fig. 3 is a block diagram of a receiver suitable for the systemillustrated in Fig. 1.

Referring to the drawing, Fig. 1 shows equipment located at two spacedstations A and B for the transmission and reception of signals betweenthe two stations. Such signals may be transmitted in any suitablemanner. However, for the purpose of discussion, it will be assumed thatthe stations A and B are connected by electric power lines comprisingconductors LI and L2 which are to be employed for guiding signalsbetween the two stations. A system of this type is commonly referred toas a power-line carrier system.

7 component Ee cos 211st and the signal component transformer 3 to aphase shifter 3. The phase shifter 5 is designed to supply to theprimary windings IA and 9A of two transformers 1 and 9 two carrierphase-components which are displaced from each other by a substantialangle. For example, this angle may be in the range of 60 to 90". Foroptimum performance, however, it is desirable that the angle ofdisplacement be substantially 90. For example, the phase shifter 5 maybe designed to apply to the primary winding 1A of the transformer 1 aquantity represented by the expression Ec cos 21kt, wherein Ec is aconstant amplitude factor, fc represents the car rier frequency. and trepresents time. The phase or for telemetering, or for supervisorycontrol purposes, or it may be a voice signal. For present purposes, itwill be assumed that a voice signal is provided by means of a microphoneIS, the output of which may be amplified, if necessary, by means of anamplifier H. The output of the amplifier I! is coupled through atransformer l9 to a phase shifter 2|. This phase shifter is designed toproduce two signal components which are displaced in phase bysubstantially the same angle of displacement present between the twocarrier components supplied by the transformers,

l and 9.

For example, let it be assumed that a signal having a frequency '1' issupplied through the transformer I9 to the phase shifter 2|. The

phase shifter then may be designed to provide an output between theconductors 23 and 25 which is represented by the expression -E. sin21rfst,

wherein Es represents an amplitude factor. In addition, the phaseshifter provides an output between the conductors 21 and 26 which may berepresented by the expression E- cos 21kt. By

E cos 21m. Consequently. if the modulator I is of the balanced type, theoutput thereof may be represented by the expression (E0005 211st) (E-cos 214.0. This expression represents the sum of the two side bandsproduced by the modulator and may be represented by the expression In asimilar manner the modulator l3 has applied thereto the two componentsrepresented by the expressions Ec sin 21kt and E. sin 211st. If themodulator I3 is of the balanced type. its output may be represented bythe expression The output of the modulator II is applied to a loadresistor 29 through a coupling transformer 3|. Similarly, the output ofthe modulator I3 is applied to a load resistor 33 through a transformer35. I

From the foregoing discussion, it is clear that the voltage drops acrossthe resistors 29 and 33 represent respectively the sum and difference ofthe upper and lower side-bands produced by the modulators I! and I 3.Consequently, by adding these voltage drops, the resultant voltagerepresents the lower side-band. By subtracting the two voltage drops theresultantvoltage represents the upper side-band.

The resultant voltage is applied to a suitable amplifier 31. To thisend, a conductor 39 is connected to the resistors 29 and 33 throughadjustable taps 4| and 43. Each tap and its associated resistor mayconstitute a potentiometer. By suitable adjustment of the taps, theportions of the voltage drops across the resistors 29 and 33 which areutilized may be adjusted to eliminate substantially one of theside-bands. This is desirable for the reason that the circuitsassociated with the modulators II and I! may not be exactly similar.

One terminal of the resistor 33 is connected to ground through aconductor 45 and the conductor 25. One terminal of the resistor 29 isconnected through a conductor 41 to the amplifier 31. The output of theamplifier 3'I,may be coupled in any suitable-manner to the conductors LIand L2, as through capacitors 49 and 5|.

From the preceding discussion, it is clear that a single side-bandsignal is applied to the conductors LI and L2 through the capacitors 49and 5|. This signal may be picked up at the station B in any suitablemanner. As illustrated in Fig. 1, a receiver 93 suitable for receivingsingle side-band signals is coupled to the conductors LI and L2 at thestation B through phase shifter corresponding to the capacitor 59 andthe resistor 8| would produce substantially a 90 phase displacementbetween the components supplied to the primary windings IA and 9A withsubstantially equal amplitudes for only one frequency-of the oscillatorI.

It is desirable that the phase shifter be ca-v pable of producing asimilar phase shift and maintaining substantially constant amplitude ofthe components for all frequencies for which the oscillator may beadjusted. As previously pointed out, the oscillator may be designed tooperate at any frequency within the range of 50 to 150 kilocycles persecond. In order to make the phase shifter 5 effective over this entirerange of frequency, a pair of inductance coils 53 and 55 are providedwhich are mutually coupled. By reference to Fig. 1, it will be notedthat the coil 53 is-connected in series with the capacitor 58 and theresistor 6| across the secondary winding of the transformer 3.

It is well known in the art that the voltage drops across inductancecoils and capacitors vary as functions of frequency in oppositedirections. Since the coils 63 and 65 are mutually coupled, a voltage isinduced in the coil 65 which also varies as a function of frequency.However, the voltage across the coil 65 is substantially in phase withthe voltage across the capacitor 59. Since the amplitudes of thevoltages across the coil 65 and capacitor 59 vary in opposite directionsas the frequency of the oscillator l is changed, it may be observed thatthe components of the phase shifter 5 may be proportioned to. maintainthe resultant voltage across the coil 65 and the capacitor 59substantially constant over a small i range of frequency, such as arange of 50 to 150 kilocycles per second. Since the primary winding 1Ais connected for energization in accordance with this resultant voltage,the voltage applied to this primary winding 7A is rendered substantiallyconstant over the desired frequencyrange.

Further improvement in the performance of the phase shifter 5 isefiected by making the internal impedances of the two output circuits ofthe phase shifter substantially equal. To this end, a resistor 6'! isprovided which is substantially equal in value to the value of theresistor 6|. Also a capacitor 69 and an inductance coil 1| are locatedin the circuit energized by the voltage across the resistor 6|. Thecapacitor 69 and the inductance coil H correspond respectiveiy in valueto the capacitor 59 and the inv ductance introduced by the inductancecoil 65.

As representative of suitable values for the components of the phaseshifter 5, the following table is presented:

Capacitor 59 microfarad .01

Capacitor 69 do .01 Resistor 6| .r ohms 400 Resistor 61 do r 400 Mutualcoupling between coils 63 and 65 henry .0004 Coil ll do .0004

These values are suitable for a frequency range of 50 to 150 kilocyclesper second and maintain For example, in telephone conversation, it isdesirable to have a frequency range of the order of 250 to 4,000 cyclesper second. For such a range, the phase shifter 2| must handle an upperlimit frequency which is approximately 16 times a the lower limitfrequency.

Certain components of the phase shifter 2| correspond to components ofthe phase shifter 5. For example, the phase shifter 2| includesinductance coils I3, 15 and I6, capacitors l1 and 19 and resistors 8|and 83 which correspond respectively to the coils 63, 65, and 1|,the'capacitors 59 and 69 and the resistors 6| and 61 of the phaseshifter 5. The.performances of the corresponding components are similarin the two circuits, but it is to be understood that the values thereofare selected in accordance with the frequencies to be handled thereby.It may .be pointed out that the capacitance of the capacitor 59 and theinductance introduced by the coil 53 across the secondary winding of thetransformer 3 preferably should be resonated approximately to thegeometrical mean of the frequency range which is to be applied to thephase shifter. A similar comment holds for the capacitor I1 and 1 thecoil 13 of the phase shifter 2|.

all)

If only the components thus far mentioned for the phase shifter 2| wereemployed, the amplitude of the voltage applied between the conductors 23and 25 would be equal to the voltage applied between the conductors 21and 25 for only two frequencies. If the amplitudes 'of these voltageswere plotted as a function of frequency,

the curves would intersect at two points. Because of the difference inamplitudes of the voltages within operating range, the cancellation ofone side band in the system of Fig. 1 would not be as complete asdesired.

In order to improve the performance of the phase shifter 2 an additionalresistor of substantial value is connected in series with the secondarywinding of the transformer l9. This resistor may .have a valuesuflicient to maintain the current flowing through the secondary windingof the transformer l9 reasonably constant throughout the operating rangeof the phase shifter.

In addition, a parallel circuit containing an in- I effect of thisparallel resonant circuit is to cause the curves representing thevoltage between concluctors 23 and 25 and the voltage between theconductors 21 and 25 to approach each other more a closely over thedesired range. For example they may intersect at four points over thefrequency range applied to the phase shifter 2|. The deviation betweenthe two curves at any point is small enough to assure excellentoperation of the system. Moreover, the phase displacement between thetwo components is maintainedsubstantially uniform. In a phase shiftersimilar to the phase shifter 2|, tests have shown that it is possiblewith a range of input frequency of 250 to 4000 cycles per second tomaintain the voltage outputs of the phase shifter balanced in amplitudewithin 4%, and constant in phase displacement within one degree of overthe entire range.

The value of the resistor 85 may vary over a substantial range or theresistor may be omitted completely. Preferably, the value of theresistor 33 is selected to maintain the phase angle between the twooutput phase components of the phase shifter approximately 90 over awide range of frequency; To this end, if the phase shifter isdesignedfor a 90 phase angle, the resistor 85 should have a valueselected to make the phase angle substantially 90 at the limits of thefrequency range to be handled by the phase shifter.

As examples of suitable values for the componentsof the phase shifterII, the following table is presented:

The coils may have a Q of 18 measured at a frequency of 1000 cycles persecond.

The modulators II and I3 may be of any suitable type. However, it isdesirable that balanced modulators be employed in order to suppress thecarriers supplied thereto from the phase shifter 3. Although electronictube modulators may be employed, barrier-layer modulators offer a numberof advantages. Not only do they eliminate power sources, such as heatertransformers and plate voltage supply sources, but they have extremelygood modulation characteristics for single side-band work. In addition,the balance thereof may be adjusted by application thereto of directcurrent as hereinafter pointed out.

The most common barrier-layer rectifiers in use today are those known asselenium and copper-oxide rectifiers. have been particularlysatisfactory for the modulators II and I3. They may be arranged invarious ways as well known in the art. However, in Fig. 1, eachmodulator is of the ring type and employs four copper-oxide rectifiers9|, 92, 93 and 95. As clearly shown on the drawing, each successive pairof copper-oxide rectifiers has a terminal disposed therebetween forconnection to associated transformers. It will be noted that the fourcopper-oxide rectifiers are arranged substantially in a bridge. If eachbridge is balanced, no carrier should appear in the output transformers3| and 35. However, if a bridge is unbalanced, as by reason of inherentvariations in the copper oxide rectifiers, some carrier may appear.

In order to balance or unbalance the modulators as desired, directcurrent is supplied thereto from a source represented by conductors L3and L4. These conductors have two potentiometers 91 and 99 connectedthereacross. The potentiometers respectively have adjustable taps I andI03 associated therewith. The tap IOI is connected through a resistorI08 and the conductor 23 to a center-tap 90 on the secondary winding 93of the transformer 9. Similarly, the tap I03 is connected through a'resistor I and the conductor 21 to a center-tap won the secondarywinding [3. In addition, a resistor I0'I having a grounded center-tap isconnected between the conductors L3- and L4. Center-taps on the primarywindings'of I of current therethrough, thIs tends to unbalance thebridge represented by the modulator I I, and

Copper-oxide rectifiers I 9 from the phase shifter 3.

the transformers 3| and 33 are connected to ground.

A rectifier of'the copper-oxide type has a resistance which variesinversely with the current flowing therethrough. Let it be assumed thatthe tap I03 is adjusted to make the center tap IC positive with respectto the center-tap 3IC.

0 Under these circumstances, current flows through the copper-oxiderectifiers 33 and 93. Since the resistance of such rectifiers varies asa function the extent of unbalance depends on magnitude of the voltageapplied between the terminals IC and 3IC. The value of the voltage. inturn, is dependent on the adjustment of the tap I03;

Let it be assumed next that the tap I03 is adjusted to make the tap 'ICnegative with respect to the tap 3IC. Under such circumstances, directcurrent will flow through the copper-oxide rectiflers 93 and 3|. Thistends to unbalance the bridge, represented by the modulator I I in theopposite direction, and the extent of unbalance is adjusted byadjustment of the tap I03.

From the foregoing discussion, it will be clearly apparent that if noaudio signal is supplied to the modulator I I, the carrier output of themodulator may be substantially suppressed by proper manipulation of thetap I03. In a similar manner, the tap |0| may be manipulated to adjustthe modulator I 3.

Incertain cases, it may be desirable to unbalance deliberately one ofthe modulators. For example. in relaying work, operation of a relay maybe employed for placing a carrier signal on the conductors LI, L2. Sucha carrier signal may be produced by deliberately unbalancing one of themodulators II or I3. For example, operaexample, the voltage drops acrossthe resistors 29 and 33 may be connected either additively orsubtractively, depending upon the specific sideband desired. Theside-band employed also may be changed by interchanging the connectionsof one of the transformers 3| or 35. or by interchanging the conductors23 and 21, or by interchanging the inputs to the transformers I and Ifdesired, the transformers 3| and 35 may be combined, thereby, providinga single secondary winding for connection to the amplifier 31. In thiscase, the inputs to the two modulators may be adjusted for balancingpurposes. However,

the preferred embodiment is that illustrated in Fig. 1.

If it is desired to employ the upper and lower side-bands for separatepurposes, connections similar to those illustrated in Fig. 2 may beemployed. Referring to Fig. 2, it will be observed that two transformers3IA and 35A are shown. These transformers correspond, respectively, to

I the transformers 3| and 35 of Fig. 1, and the primary connectionsthereof may be exactly the same as those illustrated for thetransformers 3| and 33. It will be observed. however, that thetransformer 3| has two secondary windings I|3 and H1. The transformer35a also has two secondary windings H9 and I2I. By tracing theconnections it will be observed that the windings H5 and H9 areconnected in series opposition across the input of an amplifier I23. Thesame windings are connected in aiding series relationship across theinput of an amplifier I25. In a somewhat similar manner, the windingsIII and I2I are connected in series opposition across the input to theamplifier I23, and in series aiding relation across the input to aconsideration of Fig. 2, it will be clear that each of the amplifiersI23 and I25 supplies a separate one of the side-bands produced by thesystem of Fig. 1, I

For amplifying purposes, any suitable amplifier may be employed. Asshown in Fig. 1, the amplifier 31 includes two pentode tubes I21 and I29having plate electrodes I21a and I290, respectively, connected through asuitable plate resistor I29b and an inductance coil I2'Ib to a commonconductor I3I. This conductor I3I is connected to the positive terminalof a source of direct voltage. The negative terminal of the source isconnected to ground. The screen grids I210 and I290 of the pentodes alsoare connected to the conductor I3I. The suppressor grid I21d and cathodeI21e of the pentode I21 are connected through a cathode resistor I21fand a bypass capacitor I21g to ground. In an analogous manner, thesuppressor grid I29d and the cathode I296 of the pentode I29 areconnected to ground through a cathode resistor I29 and a bypasscapacitor I299.

The input to the amplifier the conductor 41 which is connected to trolgrid I29h of the pentode I29. the pentode I29 is coupled through acoupling capacitor I33 to the control grid I21h, and a grid resistorI219 associated with the pentode I21. The output of the pentode I21 isapplied through a coupling capacitor I35 to a parallel tuned circuitcomprising an inductance coil I31 and a capacitor I39. This paralleltuned circuit is tuned substantially to the output frequency of theamplifier. The voltage across this circuit is coupled through thecapacitors M and 5I to the conductors LI and L2. As shown in Fig. l, acenter tap on the coil I31 is connected to ground.

It is'believed that the operation of the system is clear from theforegoing discussion. If it is desired to communicate by voice signalbetween the stations A and B, the voice signal is converted into acorresponding audio signal by means of the microphone I5. This audiosignal is passed through the phase shifter 2| to provide two componentsdiffering in phase by approximately 90. Similarly the output of anoscillator I is passed through the phase shifter 5 to provide twocomponents also differing in phase by substantially 90. These componentsare'supplied to the ring modulators i I and I3 to producecarrier-suppressed, double side-band outputs in the secondary windingsof the transformers 3| and 35. The outputs of the transformers 3I and 35are supplied to load resistors 29 and 33 and are combined to eliminateone of the side-bands. The resulting single side-band signal isamplified in the amplifier 31 and applied to the conductors LI and L2through the coupling capacitors 49 and 5I. This single side-band signalis received by means of a suitable receiver 53 at station B. Similarequipment may be located at each station, if desired, to permittransmission of voice 31 is derived through the conthe amplifier I25. ByI The output of communication from the station B to the station A.

If it is desired to transmit a carrier signal between the stations A andB, the contacts II3 are actuated to unbalance the modulator II. Thisresults in the generation of a carrier signal which is amplified in theamplifier 31 and app e across the conductors LI and L2 for reception atthe station B.

Sometimes it is desirable to employ a standard superheterodyne receiverfor reception of Single side-band signals. A receiver of this type is11- lustrated in block form in Fig. 3.

Referring to Fig. 3, it will be noted that the incoming single side-bandsignal is represented by the sum or difference of two frequencies fc andis which are, respectively, the carrier and signal frequencies. Eitherthe sum or difference of these frequencies will be received depending onwhether the upper or the lower side-band is to be employed. The incomingsignal is mixed in a suitable mixer I4I with a frequency equal to fc+fi,wherein I1 is the intermediate frequency of the superheterodynereceiver. Consequently. the output of the mixer includes a frequencyJl-fs or f1+fs, depending on the specific sideband being received. Thisintermediate frequency is amplified in an intermediate frequencyamplifier I43 and supplied to a suitable modulator I45 which may be ineffect a second mixer stage. If automatic volume control is provided,the controlling signal for the automatic volume control should bederived from the intermediate frequency amplifier prior to demodulation.In the demodulator I45, the intermediate frequency signal is mixed withan oscillation having a frequency fl. Consequently, the desired signalfs is obtained from the demodulator I45 and may be employed to actuateany suitable translating device I41 such as a loudspeaker.

It will be noted that two specific frequencies .fc-l-fi and ii areinjected, respectively, into the mixer MI and the demodulator I45. Ifseparate sources are provided for these two oscillations, extremestability would be required for both sources. I

In order to simplify the stability problems of the receiver, a localoscillator I49 is provided which is capable of generating a frequencyfc. This local oscillator is designed to operate with great stability.Since an oscillator similar to the oscillator I of Fig. 1 normally willbe available at each station for transmitting purposes, a portion of theoutput of the oscillator I may be employed in place of the localoscillator I49.

The output of the local oscillator I49 is supplied to a'mixer ISI. Thismixer also receives an output from an oscillator I53 which generates anoscillation having substantially the frequency ,fi.

Consequently, the output of the mixer I5I provides the frequency,fc-l-fl which is required for the mixer I4I. In addition, theoscillator I53 provides an oscillation of the frequency f1 required forthe demodulator I45.

In the system of Fig. 3, the oscillator I53 need not be as stable as theoscillator I49. It will be recalled that the intermediate frequencyamplifier I43 supplies to the demodulator a, quantity represented by thefrequency fiat s. In the demodulator I45, a quantity is produced whichis represented by the expression (fizfs) f1=: :f Consequently, if thefrequency .fi varies, such variation does not affect the quantityrepresented by the frequency 2: which is supplied to the translatingdevice m. Preferably the oscillator I53 should have a stabilitysufilcient to maintain the signal 112:!- within the pass band of theintermediate frequency amplifier I43. Consequently, the receiver of Fig.8 requires great stability only in the local oscillator us. 1

Although the invention has been described with reference to certainspecific embodiments thereof, numerous modifications are possible.Therefore. the invention is broadly set forth in the appended clalms.

I claim as my invention: 1. In a system for producing a single sidebandquantity, means for producing a first carrier alternating quantity and asecond carrier alternating quantity having a. substantial phasedisplacement therebetween. said first and second carrier quantitiesbeing of the same frequency, means for producing a first modulatingquantity and a second modulating quantity having substantially saidphase displacement therebetween, means for modulating said first carrierquantity by said modulating quantity to produce a first double sidebandoutput, means for modulating said second carrier quantity by said secondmodulating quantity to produce a second double sideband output, saidmodulating means com-- prising barrier-layer modulator means, and meansfor combining said outputs to eliminate one of said sidebands.

2. In a system for producing a single sideband" quantity, means forproducing a first carrier alternating quantity and a second carrieralternating quantity having a substantialphase displacementthel'ebetween. said first and second carrier quantities being of thesame frequency, means for producing a first modulating quantity and asecond modulating quantity having substantially said phase-displacementtherebetween. means for modulating said first carrier quantity by saidfirst modulating quantity to producesa first double sideband output,means for modulating said second carrier quantity by said sec:ondmodulating quantity to produce a second double sideband output, saidmodulating means comprising balanced barrier-layer modulator meanswherein the carrier quantities are substantially suppressed, and meansfor combining said outputs to eliminateone of said sidebands.

3. In a system for producing a single sideband quantity, means forproducing a first carrier alternating quantity and a second carrieralternating quantity having a substantial phase displacementtherebetween, said first and second carrier quantities being "of thesame frequency, means for producing a first modulating quantity and asecond modulating quantity having substantially said phase displacementtherebetween, means for modulating said first carrier quantity by saidfirst modulating quantity to produce a first double sideband output,means for modulating said second carrier quantity by said secondmodulating quantity to produce a second double sideband output. saidmodulating means comprising balanced barrier-layer modulator means,means for adjusting the modulator means to eliminate substantially thecarrier quantities, and means for combining said outputs to eliminateone of said sidebands.

4. In a system for producing a single sideband quantity, means forproducing a first carrier alternating quantity and a second carrieralternating quantity having a substantial phase dis placementtherebetween. said first and second carrier quantities being of the samefrequency, means forproducing a first modulating quantity and a secondmodulating quantity having substantially said phase displacementtherebetween, means for modulating said first carrier'quantity by saidfirst modulating quantity to produce a first double sldeband output,means for modulating said second carrier quantity by said secondmodulating quantity to produce a second double sideband. output, saidmodulating means comprising balanced barrier-layer modulator means,means for adjusting the modulator means to eliminate substantially thecarrier quantities, said last-named means comprising means forintroducing direct current into the barrier-layer modulator means, andmeans for combining said outputs to eliminate one of said sidebands.

5. In an electrical system, a plurality of barrierlayer rectifiers,means connecting said barrierlayer rectifiers in. a circuit havingparallel paths, and means for adjusting the relative impedances of saidpaths, said last-named means comprising means for passing biasingcurrent through part of the barrier-layer rectifiers.

- a plurality of barrier-layer rectifiers, means connecting saidbarrier-layer rectifiers in a circuit having parallel paths eachcontaining one of the barrier-layer rectifiers, and means for adjustingthe relative impedances of said paths, said lastnamed means comprisingmeans forpassing direct current through a preselected part of thebarrierlayer rectifiers. v

'7. In a system for producing a modulated quantity, a barrier-layermodulator having a plurality of paths each containing a barrier-layerrectifier, and means for'passing direct current through at least part ofsaid paths for modifying the impedance characteristics thereof.

8. In a system for producing a modulated quantity, a bridge modulatorhaving four paths related to form abridge circuit, each of said pathsincluding a barrier-layer rectifier, and meansuor passing direct currentthrough certain of the paths for modifyingthe balance of the bridgecircuit. i

9. In a system for producing a modulated quantity, a barrier-layermodulator having a plurallty of paths each containing a barrier-layersource, and means rerectifier, a direct voltage sponsive to the polarityof the source for selecdirect current through either of tivel directing4 a pair of said barrier-layer rectifiers. 10. In a system for producinga modulated quantity, a ring modulator comprising four ringconnectedcopper-oxide rectifiers, minal intermediate each adjacent pair ofrectihere to form a resultant bridge circuit. and m ns for applying adirect voltage between a first pair on of the terminals which aredisposed on a diagonal of the bridge circuit and the remaining terminalsfor modifying the balance of the bridge'circuit, said means includingmeans for adjusting the magnitude and reversing the polarity of thedirect es voltage.

11. In a system for producing a single sideband quantity, means forproducing a first quantity representing the sum of the bands ofamodulated carrier, means for producing a second quantity representingthe difference between said upper and lower sidebands, and means forcombining said first and second quantities to eliminate one of thesidebands. said last-named means comprising an adjustable potentiometerenergized by one of the quantities for adjusting 6. In analternating-current electrical system,-

having a terupper and lower sideamaeso the relative amplitudes of thefirst and second quantities to effect substantially complete eliminationof one of the sidebands. i

' 12. In a system for producing a single sideband quantity, means forproducing a first carrier alternating quantity and a second carrieralternating quantity having a substantial phase dis- ..Dlacementtherebetween, said first and second provide an adjustable output, meansfor modulating said'second carrier quantity by said second modulatingquantity to produce a second double sideband output, said modulatingmeans comprising balanced barrier-layer modulator means for adjustingthe modulator means to eliminate substantially the carrier quantities,said last-named means comprising means for introducing direct currentinto the barrier-layer modulator means, and means for combining theadjustable output and the second double sideband output, whereby theoutputs may be adjusted relative to each other to eliminatesubstantially one of the sidebands.

13. In a system for shifting the phase of an alternating quantity, meansresponsive to an alternating input for producing a first quantity and asecond quantity having a substantial phase displacement therebetween,said first quantity varying as a function of frequency of thealternating input, means for producing a third quantity varying with thefrequency of the alternating input in a manner substantially opposite tothe variation of the first quantity, whereby the first and thirdquantities may be combined to produce a fourth quantity which issubstantially less immune to variation in frequency of the alternatinginput than said first and third quantities, means associated with saidfirst and second-named means for producing output circuits for saidsecond and fourth quantities, and means for balancing the internalimpedances of the output circuits to which the second and fourthquantities are applied.

14. In a system for shifting the phase of an alternating quantity over asubstantial frequency range, means responsive to an alternating inputfor producing a first quantity and a second quan'-- tity having asubstantial phase displacement therebetween, said first quantity varyingas a function of frequency of the alternating input, means for producinga. third quantity varying with the frequency of the alternating input ina manner substantially opposite to the variation of the first quantity,whereby'the first and third quantities may be combined to produce afourth quantity which is substantially less immune to variation infrequency of the alternating input than said first and third quantities,means associated with said first and second-named means for producingoutput circuits for said second and fourth quantities, and means formodifying the phase displacement of the second and fourth quantitiesadjacent the limits of the frequency range for which the phase shifteris designed.

15. In a system for shifting the phase of an alternating quantity, meansresponsive to an alternating input for producing a first quantity and asecond quantity having a substantial phase displacement therebetween,said first quantity varying asv a function of frequency of thealternating input, means for producing a third quantity varying with thefrequency of the alternating input in a manner substantially opposite tothe variation of the first quantity whereby the first and thirdquantities may be combined to produce a fourth quantity which issubstantially less immune to variation in frequency of the alternatinginput, means associated with said first and second-named means forproviding output circuits for said second and fourth quantities, saidsecond and fourth quantities having amplitudes which when plotted as afunction of frequency have two points of intersection, and means forvarying the amplitude of the second quantity relative to the amplitudeof the fourth quantity.

as a function of frequency to provide more than two points ofintersectionthereof, whereby the difference in the amplitudes of thesecond and fourth quantities is small over a substantial range offrequency variation of the alternating input.

16. A system as defined in claim 15 wherein the last-named meanscomprises a resonant circuit tuned to a frequency within the range ofthe alternating input, said resonant circuit being connected to alterthe amplitude relationships of the second and fourth quantities as afunction of frequency.

17. In a system for shifting the phase of an alternating quantity overthe range of frequency required for intelligible speech, a circuitcomprising a capacitor, a resistor and an inductance winding connectedin series for energization from. a suitable source in accordance withthe alterwith the voltage across said resistor, said capacitor and theinductance introduced by the first named inductance winding beingresonated subternating quantity over the range of frequency required forintelligible speech, a circuit comprising a capacitor, a resistor and aninductance winding connected in series for energization from a suitablesource in accordance with the alternating quantity, a first outputcircuit including an inductance winding connected for energization inaccordance with the voltage across said capacitor, said inductancewindings being mutually coupled to'induce in the second-named inductancewinding a voltage which adds to the voltage across the capacitor toprovide a resultant voltage which is substantially constant over asubstantial range of variation in the frequency of the alternatingquantity, and a second output circuit connected for energization inaccordance with the voltage across said resistor, said output circuitshaving 15 r ing connected in series for energization from a suitablesource in accordance with the alternating quantity, a first outputcircuit including an inductance winding connected for energization inaccordance with the voltage across said capacitor,

said inductance windings being mutually coupled to induce in thesecond-named inductance winding a voltage which adds to the voltageacross the capacitor to provide a resultant voltage which issubstantially constant over a substantial range of variation in thefrequency of the alternating quantity, and a second output circuitconnected for energization in accordance with the voltage across saidresistor, the series circuit connected for penergization from thesuitable source including sufllcient resistance to maintain currentsupplied thereto from the source substantially independent of frequencythroughout the operating range of the phase shifting system.

20. In a system for shifting the phase of an alternating quantity overthe range of frequency required for intelligible speech, a circuitcomprising a capacitor. a resistor and an inductance winding connectedin series for energization from a suitable source in accordance with thealternating quantity, a first output, circuit including an inductancewinding connected for'energization in j accordance with the voltageacross said capacitor; said inductance windings being mutually coupledto induce in the second-named inductance winding a voltage which adds tothe voltage across the capacitor to provide a resultant voltage which issubstantially constant over a substantial range of variation in thefrequency of the alternating quantity, and a second output circuitconnected for energization in accordance with the voltage across saidresistor, and a parallel resonant cir-' the resonant frequency of theparallel resonant circuit.

22., In a system for producing a single sideband quantity, means forproducing polyphase carrier components comprising a first carrier phasecomponent and a second carrier phase component, means for producingpoiyphase signal components comprising a flrstsignal phase component anda second signal phase component, the phase displacements between thecomponents being of appreciable magnitude and substantially equal for ithe carrier and signal, a first barrier-layer ring modulator, a secondbarrier-layer ring modulator.

cult connected for energization from said suitable source.

21. A system as claimed in claim 20 wherein the parallel resonantcircuit is tuned to resonate substantially at the geometrical mean ofthe'frequency range for which the system is designed.

and wherein the output circuits have substantially equal internalimpedances, said capacitor and the inductance introduced by thefirst-named induct-,

ance winding being resonated substantially to with one of saidcomponents to the associated one of the modulators a direct-currentquantity for modifyin the balance of the last-named modulator. 4

24. A system as defined in claim 23 wherein the balance-.control-meansis adiustable for varying the magnitude and polarity of thedirect-current quantity.

} BERNARD E. IENEHAN.

REFERENCES CITED The following references are, of record in the file ofthis patent:

UNITED STATES PATENTS 4 Number Name Date 1,666,206 Hartley Apr. 17, 19282,163,680 .Hansell June 2'7, 1939 2,173,145 winner Sept. 19, 19392,191,315 Guanella Feb. 20, 1940 2,400,133 Pray May 14, 1946 M iddelJan. 14, 1947

